v0.3.1

Bug fixes

• Stacked layout gap inflation — when max_width triggered vertical stacking, gap expansions computed for the wide layout were incorrectly reused, adding excessive vertical space between every node pair
• Mindmap multi-line labels — labels containing \n were inserted raw into connector strings, breaking line alignment. Now joined with · for inline display
• Gap expansion limited to source/target layers only — intermediate gaps that just carry straight vertical lines no longer get inflated